I. Field of the Invention
The present invention is directed to control of transmit signal power using digital representations of expected output power.
II. Description of the Related Art
In signal transmission systems it is important to maintain expected power levels in transmit signals. For example, in code division multiple access (CDMA) cellular systems, performance is dependent on accurate control of radiated power from both subscriber units and base stations. The precise level of radiated power for the forward link serves to balance the forward and reverse link boundaries of a sector or cell. This, in turn helps to reduce the size of hand-off regions, increase overall system capacity and improve subscriber performance in the hand-off region. In addition, industry standards require that the total transmitted power remain within +2 dB and -4 dB of the nominal power rating.
In order to maintain the forward transmit power at a desired level it is necessary to implement a mechanism that compensates for unintentional gain fluctuations observed in various components of the transmit chain. Unintentional variations can be caused by drifting operating points resulting from aging, changes in the ambient temperature, air pressure and humidity levels. Other contributing factors such as saturation of amplifiers and changes in the traffic load (i.e., desired power level) can be included. Calibration procedures do not generally ensure precise levels of output power over time. A signal-based control system that compares an expected output level to the actual output level is desired.
In addition to unintentional power fluctuations, many types of signal transmission systems intentionally vary or fluctuate output power. For example, in CDMA systems, output power levels are intentionally varied based upon such factors as, for example, the number of active mobile units, the amount of traffic to each mobile unit, and the location of mobile units. Moreover, each channel in a CDMA system can have an independent expected power level. In many of the channels, such as in forward traffic channels, expected output power levels can vary from frame to frame. Thus, one of the difficulties that is encountered in such systems is distinguishing between intentional fluctuations and unintentional fluctuations.
What is needed is a system, method and computer program product for compensating for unintentional power fluctuations.